- add cmake options OGS_USE_EIGEN, EIGEN_NO_DEBUG
- let Eigen initialize matrices by zero
delete MathLib/DataType.h
include Eigen
make ExtrapolationGaussQua independet of particular vector types
make ShapeData independet of particular matrix type
add MeshElement, ShapeData as template parameters to NaturalCoordinatesMapping
make TemplateIsoparameteric independent of particular matrix and vector types
QUAD4 is partial specialization
test fixed size and dynamic Eigen matrices